Generally, the present invention relates to semiconductor laser bars assembled in an array to produce a two dimensional array of output beams and, more particularly, to an arrangement of laser bars that provides for higher thermal conductivity of the assembled laser bars while optimizing their combined brightness.
In the manufacture of assembled semiconductor laser bars, it is customary to stack mount a plurality of laser bars with their respective submounts, as illustrated in U.S. Pat. No. 4,716,568 to Scifres et al. In laser bar stacks, the laser bars are respectively mounted on a submount and the submounts with bonded laser bars are stacked in a repetitive arrangement, possibly interspersed with heat spreaders. This is generally termed a "rack and stack" approach to forming a two dimensional array of laser emitters. The combination of a laser diode bar, a submount and a heat spreader may have a thickness of about 1 mm or more. Thus, the pitch between adjacently stacked laser diode bars may typically be between about 1 mm to 2 mm. The stacking of multiple bars provides a two dimensional array of laser emitters with a pitch between emitters of adjacent bars equal to the thickness of the laser bar/submount arrangement.
Rather than using the "rack and stack" approach, others have suggested the use of a heatsink mount or substrate with a plurality of spatially disposed grooves that are parallel with one another as well as perpendicular with the planar extent of a major surface of the mount in which the grooves are formed. A laser bar is inserted in each groove with its emitters aligned along or extending out of the major surface of the bar facing in a direction away from the grooves. Examples of this "bars in grooves with perpendicular emission" approach are disclosed in U.S. Pat. Nos. 5,040,187; 5,128,951; 5,284,790; and 5,311,535 to Karpinski.
There is a problem with both the "rack and stack" and the "bars in grooves with perpendicular emission" approaches in that the smallest pitch between adjacent laser bars has a lower limit. Thus, it is not possible to improve the density of the two dimensional array of emitters by reducing the dead space between adjacently disposed laser bars. Therefore, it is difficult to improve the optical quality of the total combined beam output, particularly to further enhance the brightness of the output achieved through higher emitter density.
A second problem with the both the "rack and stack" and the "bars in grooves with perpendicular emission" approaches is that the thermal performance of the two dimensional array is limited by dissipating heat from the laser bars principally via the rear regions of the laser bar submounts. As a result, a large pitch is maintained between adjacently mounted laser bars in order to achieve adequate cooling of the bars.
Therefore, there is a need to provide a laser diode array system which produces an output having low size-divergence product and where the dead space between the beams produced by adjacent laser bars is reduced. There is also a need to provide a two dimensional output beam array that permits closer inter-beam spacing of emitters in adjacently mounted laser bars without requiring any change in the original thickness of the laser bars/submount arrangement. There is a further need to provide a laser diode bar array with high cooling efficiency while 2 producing closely spaced output beams from the two dimensional array. Finally, there exists a need to provide a laser diode bar array that permits superior cooling of the assembled laser bars over the cooling possible from conventional the "rack and stack" and the "bars in grooves with perpendicular emission" laser bar arrays.